We propose to develop and evaluate a novel bipedal rat model of the manipulable spine lesion (the subluxation). Well-designed animal models is of this spine lesion are sorely needed to evaluate outcomes that are predicted by current theoretical models explaining the mechanism of spinal manipulation. Our group has recently designed and collected data on a quadruped rat model of the manipulable lesion that is providing very interesting information. Although the quadruped model has been useful, the degree to which information gained from such a model can be applied to the biped human is a question that remains unanswered. We propose to merge the unique biomechanical features of the bipedal rat with our reversible spinal fixation approach developed in the quadruped rat. This new combined model will allow us to develop a better understanding of anatomic and physiologic differences that occur largely on the basis of the bipedal stance. The resulting increased understanding of the effects of spinal fixation on the bipedal spine should increase our ability to extrapolate information gained in the animal study to clinical trials research and clinical practice. Therefore, in the proposes study, specially designed spinal attachment units (SAUs) will be surgically attached to the L4, L5, and L6 lumbar spinous processes of rats that have been prepared and, raised to walk with a bipedal stance. After post-surgical recovery, the SAUs will be externally linked for 8 weeks. The links will be applied to "fix" the vertebrae in a neutral position in one-half of the linked animals and in a flexed position in the other half. Other animals will have the links attached for 8 weeks and then removed for 8 weeks (the model permit easy "unlinking" of the spinal attachment units). Unlinking will permit us to study the effects of re-establishing motion following fixation. Three age-matched controls will be used: 1) animals with the SAUs applied but not linked, 2) animals that undergo a sham SAU surgery, and 3) animals that have no spinal surgery at all. Biomechanical testing will evaluate relative spine stiffness in all animals: All animals will be euthanized and the zygapophysial joints will be studied macroscopically for degeneration (osteophyte development, articular surface roughing, pitting, elevations, and remodeling). Lastly, the spinal cord will be examined for changes in two neuropeptides substance P and calcitonin gene related peptide. Pending the results of the proposed study, we will submit an R0I grant application to evaluate the effectiveness of spinal manipulation as a treatment for segmental spine stiffness, joint degeneration, and neurophysiologic changes using the bipedal spinal fixation model. This progressive plan of study will permit evaluation of biological mechanisms thought to link the manipulable lesion (subluxation) with spinal manipulation and the chiropractic clinical experience.